Since various polymer compounds whose skeleton is an aromatic compound are excellent, for example, in thermal resistance, radiation resistance, corrosion resistance, and mechanical strength, they are used, for example, as engineering plastics or super-engineering plastics. In particular, since aromatic polyamides show high crystallinity, they play an important role as a high-performance fiber material.
Although dicarboxylic acids are low in reactivity, since aliphatic diamines are moderate in nucleophilicity, aliphatic polyamides, such as 6,6-nylon, can readily be obtained by heating a salt of an aliphatic diamine and an aliphatic dicarboxylic acid, to carry out a dehydration reaction. On the other hand, aromatic diamines are low in nucleophilicity, and therefore it is difficult to obtain a high-molecular weight polyamide by heating a combination of an aromatic diamine with an aromatic dicarboxylic acid. Therefore, conventionally, to produce aromatic polyamides, for example, the following techniques are known: (1) a method wherein an aromatic acid chloride that is the most reactive among carboxylic acids is reacted with a diamine; (2) a direct polycondensation method, wherein a dicarboxylic acid and a diamine are reacted in the presence of a condensation agent, such as triphenyl phosphite; (3) a method wherein a polycondensation is carried out using amino groups activated, for example, with N-acetyldiamine and a dicarboxylic acid; and (4) a method wherein an aromatic diamine is converted to diacetamide, and then this diacetamide and an aromatic dicarboxylic acid are heated to a high temperature of 200.degree. to 350.degree. C., to effect amide exchange. In any of these methods, unstable and expensive compounds, such as aromatic dicarboxylic acids, activated diamine compounds, and dicarboxylic acid compounds, must to be used as raw materials.
On the other hand, a method is suggested wherein a dihalogen compound, such as an aromatic dibromide and an aromatic diiodide, is used as a raw material, and the dihalogen compound and a diamine compound are condensed by using a palladium complex catalyst under a carbon monoxide atmosphere, with carbonylation being effected (M. Yoneyama, M. Kakimoto, and Y. Imai, Makromol., 21, 1908 (1988)). Although this method is advantageous over conventional methods, in that an aromatic dihalide that can be readily synthesized is used as a raw material and the reaction conditions are moderate, the method nonetheless requires improvement because, for example, an expensive palladium complex is used as a catalyst, and also the molecular weight of the produced polymer is not fully satisfactory.